1. Field of the Invention
The present invention relates to an evacuatable package for sealing an element, such as a micromechanical vibratory gyroscope, in an evacuated space, to an evacuated package containing such an element, and to a method for producing such an evacuated package.
More particularly, the present invention relates to an evacuated package comprising a substrate, a lid portion joined onto said substrate, an evacuated space formed by said substrate and said lid portion, an element formed on said substrate and contained in said evacuated space, and a connecting hole connecting said evacuated space with an opening formed on the top face of said lid portion.
2. Description of the Related Art
FIG. 5 shows an example of a package structure for sealing a vibrating element, such as a micromechanical vibratory gyroscope, in an evacuated space. This evacuated package is composed of: a substrate 1 made of silicon, for example; a lid portion 2 to be anode-coupled with the substrate 1; and a vibrating element 4 (e.g., a micromechanical vibratory gyroscope) formed on the substrate 1 and accommodated in a space 3 formed by the substrate 1 and the lid portion 2.
The lid portion 2 has a connecting hole 5 connecting the space 3 to the outside for exhausting excess gas from the space 3 after anodic bonding the substrate 1 and the lid portion 2. The connecting hole 5 is closed with a sealing film 6 formed by sputtering, electron-beam deposition, or the like so as to seal the space 3 to maintain a vacuum.
The vibrating element 4 is a fine element produced by a semiconductor-device fabrication technique and its operational characteristics deteriorate in the atmosphere due to air-dumping. By sealing the vibrating element 4 in the evacuated space 3 maintained under a vacuum as described above, the vibrating element 4 can vibrate without the influence of air-dumping, and thus deterioration in the operational characteristics of the vibrating element 4 caused by air-dumping is prevented.
However, according to the above structure in which the connecting hole 5 is closed with the sealing film 6, a disadvantage is that the vibrating element 4 cannot be reliably vacuum-sealed, a fact which is attributed to the following: Since the connecting hole 5 is made in the lid portion 2 by a piercing technique such as ultrasonic processing or sandblast processing, the inner face of the resulting connecting hole 5 is rough, or in other words, has concave portions and convex portions. Furthermore, with respect to the face to which the connecting hole 5 opens, the inner face of the connecting hole 5 is tapered, as is shown in the figure, or perpendicular (not shown in the figure). Thus, it is difficult to perfectly form the sealing film 6 on the inner face of the connecting hole 5 by sputtering, electron-beam deposition, or the like. In other words, the sealing film 6 is formed on convex portions and not formed on concave portions of the inner face of the connecting hole 5 so that the inner face of the connecting hole 5 cannot be entirely covered with the sealing film 6. Thus, the space 3 is not perfectly sealed by the sealing film 6 and the air-tightness of the space 3 deteriorates, thereby decreasing the reliability of the vacuum-sealing of the vibrating element 4.
The present invention is aimed at solving the above problems. Accordingly, the present invention is related to an evacuatable package in which an element can be readily sealed in an evacuated space with improved reliability while exhibiting excellent operational characteristics. The invention is further related to an evacuated package containing such an element, and to a method for producing such an evacuated package.
The invention provides an evacuatable package of the above mentioned kind, which is characterized in that a metal film is formed on the top face of said lid portion around the periphery of said opening of said connecting hole, and a thermo-melting material is joined to said metal film to close said opening of said connecting hole.
According to the present invention, the metal film can completely cover the peripheral region of the opening of the corresponding connecting hole which opens at the top face of the corresponding lid portion, because the metal film is formed around the complete peripheral region of the opening of the corresponding connecting hole. Thus, the thermo-melting material and the metal film can be joined without forming spaces therebetween, so the space accommodating an element can reliably be evacuated and sealed to maintain a vacuum by closing the openings of the connecting holes. Thus, it is possible to greatly increase the air-tightness of the space and the element can be vacuum-sealed with greatly improved reliability.
In the above evacuated package, either said substrate or said lid portion may be composed of a glass material and the other may be composed of silicon.
In an evacuated package in which either the substrate or the lid portion is formed of a glass material and the other is composed of silicon, the substrate and the lid portion can be stably joined by anodic bonding. Therefore, the lid portion can be prevented from being stripped off of the substrate, resulting in more reliable element packaging.
The invention also provides a method for producing an evacuated package, comprising the steps of: (1) forming said opening of said connecting hole on the top face of said lid portion and a metal film on the top face of said lid portion around the periphery of said opening of said connecting hole; (2) arranging said lid portion having said connecting hole above said substrate having said element so as to accommodate said element in the space formed by said substrate and said lid portion; (3) joining said substrate to said lid portion; (4) evacuating said space accommodating said element through said connecting hole connecting said space; (5) closing said opening of said connecting hole by joining degassed thermo-melting material to said metal film so as to seal said space accommodating said element to maintain a vacuum.
In a method for producing an evacuated package incorporated in the present invention, the degassed thermo-melting material is pressed to the metal film, formed around the periphery of the opening of a connecting hole, and joined thereto so that the opening the connecting hole is closed and the space accommodating an element is sealed to maintain a vacuum. Therefore, the gas generated from the thermo-melting material is prevented from entering the space through the corresponding connecting hole, and the space is readily sealed to maintain a vacuum in which the element exhibits excellent operational characteristics. The operational characteristics of the element can be thereby improved.
The above method may further comprise the steps of: (1) preparing a second substrate, used for placing said thermo-melting material, having a dent formed in a region corresponding to said opening of said connecting hole; (2) placing said thermo-melting material in said dent on said second substrate, melting said thermo-melting material by heat, and leaving said thermo-melting material until it is substantially completely degassed, advantageously during the evacuating step; and (3) pressing said second substrate to the top face of said lid portion with said thermo-melting material in said dent and said opening of said connecting hole facing each other in the step of closing said opening of said connecting hole.
In the above method, a second substrate having a dent formed in a region corresponding to the opening of a connecting hole is prepared beforehand, and then, the thermo-melting material is placed in the dent and melted by heat for degassing. With the degassed thermo-melting material in the dent facing the openings of the connecting holes, the second substrate having the thermo-melting material thereon is pressed to the lid portion so that the thermo-melting material is pressed to the metal film around the periphery of the opening of the connecting hole and joined thereto. The positioning of the thermo-melting material at the time of pressing the thermo-melting material to the metal film around the periphery of the opening of a connecting hole thereby becomes easier. As a result, the opening of the connecting hole can be more reliably closed with the thermo-melting material and the element yield can be improved.
In the above method, a plurality of said elements may be simultaneously formed on one initial substrate while a plurality of said lid portions each having a concave portion in a region corresponding to said element may be formed in one initial lid substrate; the initial lid substrate may be joined to said initial substrate such that each element faces the corresponding concave portion and is packaged by said initial substrate and the corresponding lid portion; and said initial substrate and said initial lid substrate may be cut along predetermined dicing lines to make a plurality of said substrates and said lid portions so as to separate and complete the vacuum-sealed elements.
Since a plurality of connecting hole openings can be simultaneously closed with the thermo-melting material, the operational time required for sealing the connecting holes can be reduced and mass-production of the packaging structure becomes possible.